How to do string concatination in pl/sql

Question

I am trying
IF LENGTH(v_final_string) < 3800 THEN
        SELECT nvl2(v_final_string,v_final_string
          ||',' ,v_final_string)
          || temp.temp_string
        INTO v_final_string
        FROM DUAL;
        DBMS_OUTPUT.put_line ('v_final_string=' || v_final_string );
      ELSE
        EXIT;
      END IF;inside a loop. But it's not concatenating. I am alwas getting empty v_final_string

Answer 1

Hi,
Mr Lonely wrote:
Sorry ..
Here is my full codeThat's still not a complete script. You need to post CREATE TABLE and INSERT statements for any tables it references, or else modify it so that it uses commonly available tables, such as those in the scott schema.
CREATE OR REPLACE
FUNCTION fn_test(
v_id IN VARCHAR2)
RETURN VARCHAR2
IS
v_final_string VARCHAR2(4000) := '';
BEGIN
FOR temp IN
(SELECT name FROM test_name WHERE id=v_id
LOOP
DBMS_OUTPUT.put_line ('temp=' || temp.name );
IF LENGTH(v_final_string) < 3800 THEN
SELECT nvl2(v_final_string,v_final_string
||',' ,v_final_string)
|| temp.name
INTO v_final_string
FROM DUAL;
/* v_final_string:= NVL2(v_final_string,v_final_string|| ',',v_final_string) || temp.name;  */
DBMS_OUTPUT.put_line ('v_final_string=' || v_final_string );
ELSE
EXIT;
END IF;
END LOOP;
RETURN NVL(v_final_string,'No string Available');
END;
/Here's how you can modify it, using the second approach I suggested earlier:
CREATE OR REPLACE
  FUNCTION fn_test(
      v_id IN VARCHAR2)
    RETURN VARCHAR2
  IS
    v_final_string VARCHAR2(4000) := '';
  BEGIN
    FOR temp IN
    ( SELECT    ename     AS name
      FROM      scott.emp
      WHERE      deptno = v_id
      ORDER BY  ename -- You probably want an ORDER BY clause here
    LOOP
      DBMS_OUTPUT.put_line ('temp=' || temp.name );
      v_final_string := v_final_string
                      || ','
                      || temp.name;
      IF  LENGTH (v_final_string) >= 3800
      THEN
           EXIT;
      END IF;
      DBMS_OUTPUT.put_line ('v_final_string=' || v_final_string );
    END LOOP;
    RETURN  NVL ( LTRIM (v_final_string, ',')
                  , 'No string Available'
  END fn_test;
SHOW ERRORSSince there are 2 ways to exit the loop, I moved LTRIM outside the loop.
If you're using Oracle 11.2, the built-in function LISTAGG will be faster, if not quite as convenient.
Even in versions 9.1 through 11.1, you might consider not using PL/SQL for this. See this page for several string aggregation techniques.